AES E-Library

AES E-Library

Estimates of Nonlinear Distortion in Feedback Amplifiers

A method is proposed for characterizing nonlinear distortion in feedback amplifiers by means of two generators at the input - one voltage and one current. These generators are the negatives of the voltage and current antidistortion which, added to voltage-source and current-source input, respectively, would reduce the output distortion to zero. Their values can be calculated easily from known variations of small-signal parameters such as transistor gm, ß, and the capacitances. The distortion-to-signal ratio is given by formulas similar to the offset-to-signal ratio or noise-to-signal ratio, and depends only on the distortion generators, the signal source, and the source impedance. The method correctly predicts harmonic and intermodulation distortion for practical amplifiers. It points toward techniques for reducing distortion, and it explains certain experimental results which hitherto have been problematical.